<!DOCTYPE HTML>
<html lang="en">
<head>
     <meta charset="UTF-8">

<!-- 最新版本的 Bootstrap 核心 CSS 文件 -->
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">

<!-- 可选的 Bootstrap 主题文件（一般不用引入） -->
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap-theme.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">

<!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
<script src="https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
body { margin-left:auto; margin-right:auto; width:50em; }

    </style>
</head>
<body>
   <div class="containre">
   <div class="jumbotron">
<ul class="nav nav-pills">
  <li role="presentation" class="active"><a href="#">Home</a></li>
  <li role="presentation"><a href="#">Profile</a></li>
  <li role="presentation"><a href="#">Messages</a></li>
</ul>
<h1>hello world</h1>
<p>This is a simple hero unit, a simple jumbotron-style component for calling extra attention to featured content or information.</p>
  <p><a class="btn btn-primary btn-lg" href="#" role="button">Learn more</a></p>
<div class="alert alert-success" role="alert">
  <a href="#" class="alert-link">Well done! You successfully read this important alert message.</a>
</div>
<div class="alert alert-info" role="alert">
  <a href="#" class="alert-link">Heads up! This alert needs your attention, but it's not super important.
</a>
</div>
<div class="alert alert-warning" role="alert">
  <a href="#" class="alert-link">Warning! Better check yourself, you're not looking too good.</a>
</div>
<div class="alert alert-danger" role="alert">
  <a href="#" class="alert-link">Oh snap! Change a few things up and try submitting again.</a>
</div>
</div>
</body>
</html>
